docs: def validate(self, strict=True):
          """ check if this Swagger API valid or not.
  
          :param bool strict: when in strict mode, exception would be raised if not valid.
          :return: validation errors
          :rtype: list of tuple(where, type, msg).
          """
  
          result = self._validate()
          if strict and len(result):
              for r in result:
                  logger.error(r)
              raise errs.ValidationError('this Swagger App contains error: {0}.'.format(len(result)))
  
          return result